This is a description of what I did to add this
feature on my 1998 BMW M3. I recommend thinking
through what you are doing very carefully before actually doing anything.
Take your time, and double check everything you do. I won't be held
responsible for anyone attempting this on their own. You cut, drill,
bend, burn, melt or break pieces of your car at your own risk.

I am also assuming some basic
knowledge of wiring and automotive modification. I don't describe every
step in minute detail. If you don't know how to solder, stop here and get someone to help
you. If you don't know how to remove interior trim pieces, stop now and
get someone to help you.

Introduction

Ok, I wanted a blue
interior. I like blue, plain and simple. That BMW orange interior
is just too blah for me. I started with the sunroof switch because it
was easy to get to, and I figured if I blew something up, that would be the
cheapest component to blow up, and the least necessary (Its winter! No
need for sunroof!).

Parts

I got everything from Radio
Shack. I already had a soldering iron and solder, but
both are cheap from Radio Shack.

1 - 5mm, 300 mcd, 5 V, 30
mA blue LED

Basically, the stock orange
LEDs are replaced with an LED color of your choice. This example is
blue. In this example, a comparatively large LED is used. I
recommend using the right size, which may be found at http://www.eled.com.
I believe the 3mm is the correct size. You are on your own as far as the
electrical specs of these components. I believe the stock ones to be 4
or 5 volts, 20-40 mA, 200-300 mcd, but these are just estimates. In this
specific example, a 5V, 30 mA, 300 mcd blue 5mm LED was used. This size
will not work in the radio, instrument cluster, OBC or climate control, but
should work in all the switches.

Access the sunroof switch area
by removing the interior panel that holds the switch. Disconnect the
switch from the connector, and push the switch out of the interior panel from
the backside. You will have this:

Next, remove the outer switch
housing by pressing in the metal tabs on either side:

Insert a small screwdriver in
the opening between the yellow insert and the black housing just behind the
blue arrows above and pry the black housing away from the yellow insert, allowing the small tabs marked with an x below to unlatch
from the openings marked with a blue arrow below, on both sides.
(modification already complete, as seen by the large clear LED below, rather
than a small orange LED)

Remove the switch assembly from
the yellow insert and examine:

In the picture above, it is an
unfortunately blurry view of the bottom of the assembly. The two solder
points marked with arrows above are where the LED leads connect, positive and
negative. Heat the solder points and use pliers at the same time to pull
at the LED to remove it. Be very careful what you are doing! You
don't want to unsolder/cause a short by heating the wrong bits or being
jittery! Use a third pair of hands like a vise if you can't be very
careful! A small tip soldering iron helps.

Remove both leads of the
original orange led.

If you look at the inside of
the LED, you can see the anode and the cathode, which look different, and
compare to the new LED. Generally speaking, it seems that the LEDs you
get have a longer + positive lead and a shorter - negative lead. Your
mileage may vary. Use a watch battery to compare the two LEDs to check
for certain which is positive and which is negative. Bend the new LED
leads like the stock one, the closer the better. The new LED in the
picture above is much larger than the stock one. The stock one may be 2
mm, not 3 mm, certainly not 5 mm as above.

Position the new LED above the
holes the old one was removed from, and one at a time, resolder them to the
switch assembly. Again, be very careful when doing this. If
necessary, use a SMALL bit of solder to improve the connection.
Reassemble the switch, with the 4 prongs on the driver side of the switch,
white arrow pointing forward. You might want to connect the switch
before reassembling it, just to test your electrical skills. If you paid
attention to what you were doing, everything should work fine and it will look
something like this:

Again, please be very careful
what you are doing and take your time. You don't want to ruin any
components.

Other interior switches should
be very similar. I have not examined any others. The instrument
cluster, OBC, climate control and radio should all be similar, however I have
only examined the OBC. This will require small LEDs. Not sure if
3mm will work, and 2mm is a special order, I have not found yet.
Depending on what LEDs you get, and what their electrical specs, the effect
may be different. Some LEDs are clear, some are color diffused, like the
stock switch LED. Some are color transparent like the OBC. In the
OBC, there are plastic optical reflection panels that direct the light output
from LEDs. This could take a specific viewing angle, intensity, size,
etc. This write-up will evolve as my knowledge of the other interior bits
becomes available.